I haven't worked on a THM 200 in at least 25 years, but M10 is a very large screw for an inspection cover. Tap drill for that size will be close to 11/32" or 0.3445" If you can't make sense of the chart below [It isn't the best one I've used but it is "On-Line"] I'll try and help you out if you can post the size of the hole in the bell-housing. You can try different size drills or the "Inside jaws" on your dial caliper. I also seem to recall that many covers used more of a metal screw than machine screw. Others will likely chime in with direct knowledge. Harry https://en.wikipedia.org/wiki/List_of_d ... _tap_sizes

I'm not a hoarder I'm a preservationist 78 Monza Spyder (Soon To Be 2+2 with Spoilers)

That would be a 6mm course thread. 10mm would be the the head size. Looks like a wood screw. I have lots of them that come off the Corolla and Camrys when we make them ready at work. But, these have a large washer built on them.

I don't know if a T700R4 would be the same as your 2004R but mine takes M6 x 1 x 12mm (10mm head). Luckily the bell housing cover from my old TH350 fit straight on otherwise I'd be searching for one of those as well.http://fastenerline.com/51747-656-large ... -bolts.jpg

I also found that a #14 sheet metal screw will screw in perfectly, all the way in with just fingers. I was talking to a rep at bowtieoverdrive and mentioned it and they said that's what they always recommend to folks who ask. Who knew? LOL